The instant invention relates to apparatus and a process for monitoring respiration as well as to a conductive gel used therewith, wherein the apparatus comprises at least first and preferably second circumferential gauges that attach around a patient's abdomen and chest to monitor expansion thereof as the patient breaths. The gauges are configured as hollow tubes containing the new and improved conductive gel.
In the past, continuous volumetric monitoring of patients' ventilation generally involved use of face masks or mouthpieces, approaches which are not only invasive and uncomfortable to the patient but also interfere with the very breathing patterns being measured. These approaches required considerable cooperation from patients, which cooperation was compromised if the patient was critically ill, comatose, or very young. In addition, leaving mouthpieces in place was a danger in and of itself in that mouthpieces can suffocate patients. Utilizing these invasive methods required constant supervision and attention, further limiting the desirability of these techniques.
In view of such deficiencies, noninvasive techniques were developed such as those exemplified in U.S. Pat. Nos. 3,268,845 and 3,483,861, wherein respiration is monitored by measuring expansion of the patient's torso at primary levels of respiration; namely, expansion of the thoracic cavity, diaphragm, and abdomen. A current approach is shown in U.S. Pat. No. 4,373,534, wherein inductive loops are positioned around the thoracic cavity and abdomen. As the patient breathes, the inductive loops expand and contract, resulting in changes in cross-sectional area and inductance of the loops. Monitoring these changes provides a measure of respiration volume. This has been performed in research for a number of years, using mercury in rubber gauges. The art has continued to progress to current approaches, wherein elastic tubes containing mercury or aqueous solutions are used. Mercury is a material which should, if possible, be avoided since exposure to mercury presents a severe health hazard.
As was pointed out in Brouillette et al., "Comparison of Respiratory Inductive Plethysmography and Thoracic Impedance for Apnea Monitoring," Journal of Pediatrics, September 1987, pp. 377-383, incorporated herein by reference, respiratory inductive plethysmographs have advantages over conventional thoracic impedance monitors for infants. Plethysmographs need to be substantially modified before being used for routine monitoring of infants in hospitals or at home. Moreover, the cost is excessive and the associated systems complex.
One approach has been to use natural rubber tubes containing a conductive aqueous solution. However, rubber tubes containing aqueous solutions have been found to have a limited shelf-life of six to ten months and an active life of only 48 hours. Accordingly, they are only useful for overnight diagnostic recordings. Continuous monitoring over several days using such tubes results in considerable expense, since the tubes must be replaced repeatedly. The concept of a rubber tube with an aqueous solution has the advantage of generating very clear signals with low noise generated by physiological and electronic interference. Apparently, the shelf-life of these devices in a Mylar storage envelope and active life after the envelope is opened is limited by passage of the aqueous solution through the walls of the gauge.
Another general deficiency of prior art devices is that these devices are incapable of obtaining rapid, quantitative, absolute measurements which are accurate.
In view of the aforementioned considerations, there is a need for an improved apparatus and method which monitors respiration with accuracy and absolute values, which apparatus has signal-to-noise ratio advantages of currently available natural tubes with aqueous electrolytes, yet have both extended shelf-life and extended active life.